import { useRef, useState } from 'react';
import { GripVertical, Plus, Trash2 } from 'lucide-react';
import { Button } from '@/components/ui/button';
import { Link } from 'react-router';
import { href } from '../routes';
import type { CanvasComponent, CanvasSection } from '../canvas';
import { BandBlocks } from './BandBlocks';

/**
 * The page, as a list of its bands.
 *
 * ── Why the editor and not the nav ──
 *
 * The nav lists the same bands and is for GOING somewhere: press one and the preview scrolls to it.
 * This is for changing what the page is made of — adding a band, removing one, putting them in a
 * different order. Two different verbs on the same nouns, and mixing them would mean a nav row that
 * sometimes navigates and sometimes deletes.
 *
 * It replaced a bar painted onto the page itself, which carried the same three actions and made the
 * preview stop being a preview. See the note in canvas.ts.
 *
 * ── The gesture is the one used everywhere else ──
 *
 * Grip on the left, the row is the drop target, the list rearranges as the pointer crosses it, one
 * write at the end carrying every id. Pages, gallery items and partners all do this; a fourth way to
 * reorder something would be a fourth thing to learn.
 */
export const PageStructure = ({
  slug,
  sections,
  busy,
  onAdd,
  onDelete,
  onReorder,
  onAddComponent,
  onDeleteComponent,
  onReorderComponents,
}: {
  /** For the links: pressing a band still takes you to it. */
  slug: string;
  sections: CanvasSection[];
  busy: boolean;
  onAdd: () => void;
  onDelete: (section: CanvasSection) => void;
  onReorder: (ids: number[]) => void;
  /** A block needs a COLUMN to go in, which is the whole reason blocks are nested here. */
  onAddComponent: (section: CanvasSection, column: number) => void;
  onDeleteComponent: (component: CanvasComponent) => void;
  onReorderComponents: (section: CanvasSection, column: number, ids: number[]) => void;
}) => {
  const [dragged, setDragged] = useState<number | null>(null);
  const [order, setOrder] = useState<CanvasSection[] | null>(null);
  const pending = useRef<CanvasSection[] | null>(null);

  // The live order while dragging, or the real one. Reset whenever the page hands over a new list.
  const rows = order ?? sections;

  const moveOver = (event: React.DragEvent, overId: number) => {
    if (dragged === null) return;
    event.preventDefault();
    if (dragged === overId) return;

    const next = [...rows];
    const from = next.findIndex((one) => one.id === dragged);
    const to = next.findIndex((one) => one.id === overId);
    if (from < 0 || to < 0) return;

    next.splice(to, 0, next.splice(from, 1)[0]!);
    pending.current = next;
    setOrder(next);
  };

  const commit = () => {
    const next = pending.current;
    setDragged(null);
    pending.current = null;
    // Dropped where it started, or outside the list. Nothing moved, so nothing is written.
    if (!next) return;
    setOrder(null);
    onReorder(next.map((one) => one.id));
  };

  return (
    <div className="flex flex-col gap-2">
      <span className="text-xs font-medium">Sections</span>

      <ul className="flex flex-col gap-1">
        {rows.map((section) => (
          <li
            key={section.id}
            onDragOver={(event) => moveOver(event, section.id)}
            onDrop={commit}
            className={`flex flex-col rounded border border-border/60 ${
              dragged === section.id ? 'opacity-40' : ''
            }`}
          >
            <div className="flex items-center gap-1">
            <span
              draggable
              onDragStart={(event) => {
                setDragged(section.id);
                // Firefox starts no drag at all without data on the transfer. The value is unused.
                event.dataTransfer.effectAllowed = 'move';
                event.dataTransfer.setData('text/plain', String(section.id));
              }}
              onDragEnd={commit}
              className="shrink-0 cursor-grab py-1.5 pl-1.5 text-muted-foreground/60 active:cursor-grabbing"
              aria-label={`Reorder ${section.name}`}
            >
              <GripVertical className="size-4" />
            </span>

            {/* Still a link: pressing a band is how you get to it, here as in the nav. */}
            <Link to={href('pages', slug, String(section.id))} replace className="min-w-0 flex-1 py-1.5">
              <span className="block truncate text-xs">{section.name}</span>
              <span className="block truncate text-[10px] text-muted-foreground">
                {section.layout === 'two' ? 'Two columns' : 'One column'} ·{' '}
                {section.components.length} block{section.components.length === 1 ? '' : 's'}
              </span>
            </Link>

            <Button
              variant="ghost"
              size="sm"
              className="h-7 shrink-0 px-1.5 text-destructive"
              disabled={busy}
              onClick={() => onDelete(section)}
            >
              <Trash2 className="size-3.5" />
            </Button>
            </div>

            <div className="border-t border-border/60 px-2 py-1.5">
              <BandBlocks
                slug={slug}
                section={section}
                busy={busy}
                onAdd={onAddComponent}
                onDelete={onDeleteComponent}
                onReorder={onReorderComponents}
              />
            </div>
          </li>
        ))}
      </ul>

      <Button variant="outline" size="sm" className="h-8 self-start text-xs" disabled={busy} onClick={onAdd}>
        <Plus className="size-3.5" /> Add section…
      </Button>
    </div>
  );
};